$19.$ The application of urea can lead to nitrogen loss through $\_\_\_\_,$ a process that converts urea nitrogen to ammonia gas, which can be minimized by using urease $\_\_$ or by incorporating urea into the $\_\_\_\_.$

$-$ Options: volatilization, inhibitors, soil, leaching, activators, atmosphere

$20.$ Nitric acid is critical for the synthesis of $\_\_\_\_$ fertilizers, acting as an oxidizing agent that converts ammonia into various nitrogenous compounds, including $\_\_$ and ammonium nitrate, crucial for plant $\_\_\_\_.$

$-$ Options: nitrogen$-$based, nitric oxide, growth, phosphatic, hydrogen peroxide, respiration

$21.$ The Haber$-$Bosch process consumes a significant amount of $\_\_\_\_,$ primarily sourced from natural gas, making the production of synthetic ammonia one of the largest industrial consumers of $\_\_$ and a significant source of $\_\_\_\_$ emissions.

$-$ Options: energy, hydrogen, CO$,$ water, methane, oxygen

$22.$ Ammonium chloride fertilizer can lower the soil pH$,$ making it beneficial for crops that prefer $\_\_\_\_$ soil conditions, but its application must be managed to avoid potential $\_\_$ to plant roots and to maintain microbial $\_\_\_\_$ in the soil.

$-$ Options: acidic, damage, diversity, alkaline, benefit, stability